There is a demand for a cobalt base film (e.g., a film made of metallic cobalt, a cobalt alloy, a cobalt oxide, and a cobalt nitride) in various fields such as an electrically-conducting material field and a magnetic material field. In recent years, the cobalt alloy, e.g., a Co WP alloy, draws attention as a protective film for protecting copper wiring to be used for an LSI. A cobalt silicide that is obtained by formation of a metal Co film on Si and the subsequent heating thereof draws attention as a contact material.
In forming a cobalt base film by a chemical vapor deposition or an atomic layer control growth method, proposed examples of a source material include a cobalt carbonyl compound, a β-diketonate cobalt complex, and a cyclopentadienyl system cobalt complex.
In a case where the cobalt carbonyl compound or the β-diketonate cobalt complex, each having O (i.e., an oxygen atom) as a film-forming source material compound, are used, resulting films entrap O therein. Therefore, there is no serious problem when the cobalt film is an oxide film. To the contrary, if a target cobalt film is a metal film (including a metal alloy), there comes a problem. Also, if a target cobalt film is a nitride film, there may be a problem. Further, the cobalt carbonyl compound is a compound with CO. Therefore, in synthesizing or forming a film, it is necessary to take a measurement against toxic CO. In other words, there is a danger and a bad handling ability.
Since the cyclopentadienyl system cobalt complex does not have O (i.e., an oxygen atom), basically, the resulting film does not entrap O therein. The cyclopentadienyl system cobalt complex requires a high temperature during film formation. Therefore, the cyclopentadienyl system cobalt complex is not suitable for LSI manufacturing. Further, the cyclopentadienyl system cobalt complex has a high decomposition temperature. That means that the resulting film often entraps C therein.
In the light of the above, these days, a cobalt amidinate complex is proposed as an exemplary material for forming a Co base metal (alloy) film.
For example, a Non Patent Literature 1 (Zhengwen Li, Don Kuen Lee, Michael Coulter, Leonard N. J. Rodriguez and Roy G. Gordon, Dalton Trans., 2008, 2592-2597) and a Patent Literature 1 (JP P2006-511716 A) (WO2004/046417)) propose a compound expressed by the following general formula.

In the above general formula, R1, R2, R3, R4, R5, and R6 are selected from any one of hydrogen, an alkyl group, an aryl group, an alkenyl group, an alkynyl group, a trialkylsilyl group, a fluoro-alkyl group, or another non metal atoms or group. For example, the R1, R2, R3, R4, R5, and R6 are selected from the alkyl group or the fluoro-alkyl group, or the silyl alkyl group having 1 to 4 carbon atoms.
The Non Patent Literature 1 proposes bis(N,N′-diisopropylacetamidinate)cobalt (e.g., in the above general formula, R1=R4═CH3, R2=R3=R5=R6=C3H7).
Compounds discussed as examples in the Patent Literature 1 are bis(N,N′-diisopropylacetamidinate)cobalt (e.g., in the above general formula, R1═R4=CH3, R2═R3=R5═R6=C3H7), bis(N,N′-di-tert-butylacetamidinate)cobalt (e.g., in the above general formula, R1═R4=CH3, R2═R3=R5═R6=C4H9), and bis(N,N′-disecbutylacetamidinate)cobalt (e.g., in the above general formula, R1═R4=CH3, R2═R3=R5═R6=C4H9).
The compound (i.e., the bis(N,N′-diisopropylacetamidinate)cobalt) is made of N,N′-diisopropylcarbodimide currently used as a standard source material in a peptide synthesis field. Therefore, the compound is synthesized conveniently at low cost. Further, under high vacuum (e.g., 0.05 ton), the compound can be volatilized at a temperature of about 80° C.
The compound, however, has a melting point at 84° C. (see, Non Patent Literature 1). Therefore, if there is a cold spot in piping, solidification/blocking-up may occur during transportation of the compound. Therefore, there is a rigorous demand with respect to a temperature management of film formation equipment, which results in a reduced mass-productiveness. Further, since the compound has a solid body at room temperature, it is difficult to mass-produce the compound having high purity as a film forming material in the LSI.
A Patent Literature 2 (JP P2011-63848 A) also proposes the compound expressed by the above general formula. More specifically, the Patent Literature 2 proposes a compound expressed by the following formula (i.e., expressed in the above general formula, R1═R4=CH3, R2═R5=C4H9, R3═R6=C2H5: Co(tBu-Et-Et-amd)2).

The compound having the above formula proposed by the Patent Literature 2 has not so much problem as the problem held by the bis(N,N′-diisopropylacetamidinate)cobalt.
Whereas, a boiling point of the compound is, though it is liquid, high under high vacuum. This makes the compound difficult to volatilize. During formation of a film, an amount of source material capable of being supplied to a film forming space gets low. As a result, the optimum step coverage may not be obtained. Further, the compound has a left-right asymmetry structure. This makes it difficult to synthesize the compound and makes it expensive in manufacturing thereof.